Recent progress in the art of SAW devices provides a complex SAW filter assembly with a number of SAW filters formed on a single substrate and an RF monolithic integrated circuit (IC) assembly with a SAW device and a semiconductor IC placed on a single substrate.
However, no effective proposal has been made to acoustically isolate the respective filters from each other in the complex SAW filter assembly or acoustically separate the SAW device from the semiconductor IC in the RF monolithic IC assembly.
Prior art systems can simply reduce interference between SAW elements or between a SAW device and a semiconductor IC by arranging SAW filters so that SAW propagation paths do not cross with each other, or alternatively by interposing sound absorbing material to attenuate surface acoustic waves as shown in FIG. 5 wherein sound absorbing material 3 is imbedded in a piezoelectric substrate 1 to isolate a SAW device having a pair of comb-shaped electrodes 2 from other similar SAW devices.
The specific placement of SAW elements in the prior art to isolate the SAW propagation paths thereof unduly reduces the number of SAW filters which can be incorporated on a substrate. The use of sound absorbing material requires a high precision to properly place the material in a limited space or to maintain a uniform shape and amount of the material, and therefore causes non-uniformity in finished products.